3. Results
3.1. Cultivation of CHO-S cells in bioreactor Growth curves and viability are shown in Fig. 2. Growth rate during log
phase in a bioreactor with reciprocal mixing was not significantly
different from that in a bioreactor with rotary mixing, namely 6FT or
EE. Cell density in all bioreactors reached approximately 6.0 ×
106 cells/mL, with no significant difference across
them all (Fig. 2B). This implied that the mixing methods (rotary or
reciprocal) did not affect the growth rate during log phase or the cell
density achieved after exponential growth. However, the length of
stationary phase in reciprocal bioreactor was longer than that in both
the rotary bioreactors. Viability in 6FT and EE rotary bioreactors went
to less than 90% (~ 130 h), faster than that in
reciprocal bioreactor (160 h, Fig. 2A). Concentrations of glucose,
lactate, and leaked lactate dehydrogenase activity in culture medium are
shown in Fig. 3. Significant difference in glucose consumption was not
observed in any bioreactor (Fig. 3A). In our cases of batch culture,
consumption rate of lactate was more than its production rate when cell
growth entered the stationary phase (at approximately 80 h, Fig. 3B).
However, the concentration of lactate in reciprocal bioreactor decreased
faster than in other rotary bioreactors. This revealed that
physiological conditions of cells in all bioreactors proceeded from the
production to consumption of lactate in approximately 80 h, and at the
same time something else also changed that caused the difference in
viability during the late stationary phase. High concentration of
lactate in culture medium is detrimental for viable cells. Therefore,
the rapid consumption of lactate in reciprocal bioreactor might make
conditions more feasible for maintaining high cell viability.